In a conventional diesel electric locomotive, a thermal prime mover diesel engine is used to drive an electrical transmission. To increase a maximum amount of useful power that a locomotive engine of given size can develop when at a discrete speed, the usual practice is to equip the engine with a combustion air supercharger or turbocharger. In a typical turbocharger, a turbine is driven by engine exhaust gas. The turbine then drives a compressor that draws in ambient air and increases the pressure of intake air provided to the engine. This permits more fuel to be burned in the cylinder, and therefore the expanding products of combustion will exert more force on the piston during each power stroke. The main advantage of a turbocharger is that it increases the power output of a diesel engine. However, the addition of the turbocharger to the engine also increases that complexity of the operation of the engine and its control and maintenance.
One of the common control problems of a turbocharged diesel engine is turbocharger surge. Surge is a phenomena exhibited by centrifugal compressors of the type used in turbochargers in which the compressor becomes unstable at low compressor air flows and high boost pressures. Turbocharger surge is undesirable in engine operation and prolonged surging can lead to fatigue failure of engine components due to the large pulsations of pressure that repeatedly occur during surge.
Though techniques and apparatus are available to detect and control an engine's operation to avoid surge events, most base their detection on recording actual surge events and then provide for preventing future events.